1. Field of the Invention
The present invention relates to an improved, crimpable electrical connector and to a copper-beryllium alloy particularly suited for making this electrical connector.
2. Background
Many different crimpable electrical connectors have been developed for connecting electrical wires and other electrical contacts together. One such conventional, crimpable, xe2x80x9cfemalexe2x80x9d electrical connector 10 is shown in FIGS. 1 and 2, with FIG. 1 illustrating the connector prior to crimping and FIG. 2 illustrating the connector after crimping. In typical practice, multiple female connectors 10 are mounted in a terminal block or other device for connection to multiple xe2x80x9cmalexe2x80x9d connectors of complementary design.
As illustrated in the figures, female connector 10 includes a spring section 14 defined by a socket 16 for releasably receiving the corresponding protrusion of a complementary male connector. In addition, female connector 10 also includes a crimp section 16 for permanently attaching the connector to a wire by crimping. In the particular embodiment shown, crimp section 16 is formed by crimp barrel 20, which comprises a hollow, cylindrical section which can be crimped to securely fasten the end of a wire inserted therein.
In order that a crimpable electrical connector such as illustrated in FIGS. 1 and 2 can work properly, it must exhibit a particular combination of properties. First, spring section 14 must exhibit adequate yield strength to resist permanent set on mating with its complementary connector. This is necessary in order that spring section 14 exerts sufficient spring force to securely hold the complementary male connector in place even though the female and male connectors are repeatedly joined, separated and rejoined. Second, crimp section 16 must exhibit sufficient ductility to allow crack-free crimping. If cracks form in the crimp section on crimping, the crimped connection will fail making the connector useless.
In manufacturing connectors of the type illustrated in FIGS. 1 and 2, a high-speed automatic forming machine severs a continuous wire of desired final diameter into sections and then cold forges (cold heads) and/or machines the wire sections into desired shapes. The shaped sections are then heat-treated to enhance strength and/or hardness through precipitation hardening of the alloy forming the wire, thereby producing the final connector product.
In this connection, electrical connectors such as illustrated in FIGS. 1 and 2 are usually made from copper alloys such as C19150 or C19160 both comprising nominal 1% Ni, 0.2% P, balance Cu, with, respectively, 0.5% or 1% Pb. Such alloys are typically manufactured by a process terminating in steps of (a) cold drawing the rod to a ready to finish anneal diameter, (b) solution annealing the cold drawn rod and (c) cold drawing the solution annealed rod to final diameter. Such alloys, at final diameter, can be shaped by the connector manufacturer while still relatively soft and then be hardened and strengthened by heat treatment. Alloys of this type are used because they exhibit suitable combinations of electrical conductivity, resiliency and tensile strength.
Unfortunately, heat treated alloys of this type have comparatively poor room temperature ductilities. As a result, connectors made from such heat hardened alloys must be locally softened before they can be attached to wires by crimping or similar operations, since they will crack or break if crimping is attempted without softening. Commercially, softening is typically done by locally reheating crimp section 16 of the connector by laser, electron beam, induction, or other spot heating methodology, immediately before crimping, to anneal the crimp region while retaining full heat treated strength in spring section 14. This localized annealing step is inherently expensive and contributes significantly to the cost of using electrical connectors of this design.
Accordingly, it is an object of the present invention to provide new electrical connectors of the type illustrated in FIGS. 1 and 2, which exhibit essentially the same strength, resiliency and electrical conductivity as conventional connectors, but which also exhibit sufficient room temperature ductility so that they can be attached to wires by crimping without localized heat softening as necessary in prior art designs.
This and other objects are accomplished by the present invention which is based on the discovery that certain copper-beryllium alloys, if cold worked and heat treated in a particular manner after final solution annealing, exhibit yield strengths high enough for use as electrical connectors and yet sufficient ductilities to allow crimping without reheating for localized annealing and softening.
In particular, the present invention is based on the discovery that a copper-beryllium alloy comprising 0.15 to 0.5 wt. % Be, 0.4 to 1.40 wt. % Ni or Co or both and 0.2 to 1.0 wt. % Pbxe2x80x94if age-hardening to a 0.2% yield strength between about 60 and 80 ksi for achieving resistance to permanent set upon matingxe2x80x94will also exhibit sufficient ductility to allow crack-free crimping without localized reheating provided that the alloy is cold worked after final solution annealing by about 40 to 80% and further provided that age hardening is carried out by over-aging.
Thus, the present invention provides a new electrical device having a spring end capable of maintaining a desired spring normal force after repeated matings and a crimp section capable of being joined to a wire or other component by crack-free crimping without localized annealing of the crimp region before crimping, the device being formed from an alloy comprising 0.15 to 0.5 wt. % Be, 0.4 to 1.40 wt. % Ni or Co or both, and 0.2 to 1.0 wt. % Pb, the balance being copper and incidental impurities, wherein the device after final solution annealing is cold worked by 40 to 80% and is overaged during age-hardening so that the alloy forming the device achieves a final 0.2% yield strength between about 60 and 80 ksi. When so treated, the alloy forming the device will also typically have a ductility between about 20 and 65%, measured in terms of area reduction, more typically between about 30 and 65%.
Preferably, the alloy forming the electrical connector is overaged during age hardening so that the tensile strength of the alloy is less than about 90% of its maximum tensile strength when age peak aged. Moreover, final solution annealing of the alloy is desirably done at temperatures no higher than about 1650xc2x0 F.
In one particular embodiment of the invention, the alloy forming the connector has a minimum 0.2% yield strength of 70 ksi and a ductility of about 30%. In another particular embodiment, the alloy forming the connector has a minimum 0.2% yield strength of 65 ksi and a ductility of about 50%.
In addition to electrical connectors, the present invention also provides wire stock and bar stock useful for forming these connectors. In one embodiment, it is contemplated that this stock will be xe2x80x9cfinished to sizexe2x80x9d and age hardened by the mill before being transferred to the fabricator, with the connector fabricator simply cutting the stock to sections of appropriate length and then machining the sections into the desired shape. In this embodiment, the present invention provides wire or bar stock in the form of a continuous wire or bar, the stock being formed from an alloy comprising 0.15 to 0.5 wt. % Be, 0.4 to 1.40 wt. % Ni or Co or both, and 0.2 to 1.0 wt. % Pb, the balance being copper and incidental impurities, the alloy having been cold worked after final solution annealing by 40% to 80% and overaged during age-hardening to achieve a final 0.2% yield strength between about 60 and 80 ksi and a ductility between about 30 and 65%.
In another embodiment, it is contemplated that the mill will provide the fabricator with stock already worked to xe2x80x9cfinished sizexe2x80x9d but not final age hardened. In this embodiment, it is contemplated the connector fabricator will cut the stock to sections of appropriate length, fabricate the sections into final shape by one or more shaping steps including working and machining, and finally heat treat the fabricated sections by overaging in accordance with the present invention to achieve the desired combination of 0.2% yield strength and ductility. In this embodiment, the present invention provides wire or bar stock in the form of a continuous wire or bar, the stock being formed from an alloy comprising 0.15 to 0.5 wt. % Be, 0.4 to 1.40 wt. % Ni or Co or both, and 0.2 to 1.0 wt. % Pb, the balance being copper and incidental impurities, the alloy having been cold worked after final solution annealing by greater than 40% to 80%.
Finally, the present invention also provides a new Be-Cu alloy comprising 0.15 to 0.5 wt. % Be, 0.4 to 1.40 wt. % Ni or Co, or both, and 0.2 to 1.0 wt. % Pb, the balance being copper and incidental impurities, the alloy having been cold worked after final solution annealing by 40 to 80% and overaged during age-hardening to achieve a final 0.2% yield strength between about 60 and 80 ksi and a ductility between about 20 and 65%, more typically 30 to 65%.